Decarburization of ferrous material under low pressure at elevated temperature

ABSTRACT

Continuous metallurgical treatment, especially for decarburization treatment carried out in vacuum. Successive vacuum chambers for heat treatment at various temperatures and pressures have intermediate vacuum sealing doors and material transfer devices cooperate with the doors as material passes through the apparatus during treatment. Pressure equalization chambers may be provided at the input and output ends of the apparatus.

United States Patent [Ill 3,633,649

[72] Inventors Rolf Einar Malmstrom Porl; Simo Antero livari Makipirtti, Nakkila, both of Finland [21] Appl. No. 879,423 [22] Filed Nov. 24, 1969 [45] Patented Jan. 11, 1972 [73] Assignee Outokumpu 0y Helsinki, Finland Continuation-impart of application Ser. No. 653,180, July 13, 1967, now abandoned. This application Nov. 24, 1969, Ser. No. 879,423

[54] DECARBURIZATION OF FERROUS MATERIAL UNDER LOW PRESSURE AT ELEVATED TEMPERATURE 3 Claims, 9 Drawing Figs.

[52] U.S. Cl 164/65, 164/258,266/34V [51] Int.Cl B22d 27/16 [50] Field of Search 164/61, 62,

[56] References Cited UNITED STATES PATENTS 2,788,270 4/1957 Nisbet et al 164/61 X 2,858,586 11/1958 Brennan.... 266/34V 2,882,570 4/1959 Brennan... 164/256X 2,804,664 9/1957 Brennan 164/65 2,903,759 9/1959 Brennan 164/65 X Primary Examiner-R. Spencer Annear Attorney-A1bert M. Parker ABSTRACT: Continuous metallurgical treatment. especially for decarburization treatment carried out in vacuum, Successive vacuum chambers for heat treatment at various temperatures and pressures have intermediate vacuum sealing doors and material transfer devices cooperate with the doors as material passes through the apparatus during treatment. Pressure equalization chambers may be provided at the input and output ends of the apparatus.

PATENTED Jun 1 i912 SHEET 2 0F 6 4107576007 AMP/,Q/TT/ INVENTOR5 ATTORNEY mimmm 1 m2 $633,649

SHEET 3 [IF 6 ATTORNEY PATENTEUJANI 1 m2 3533649 SHEET 6 UF 6 INVENTORS fiau-f/m/w 4M5 r m? ATTOR NEY CROSS-REFERENCE TO RELATED APPLICATION This'application is a continuation in part of our copending application, Ser. No. 653,180, now'abandoned, Equipment for Metallurgical Continuous Treatment of Various Materials in Low Pressure and at Elevated Temperature, filed July 13, 1967.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for continuous metallurgical treatment of various materials under low pressure, or in a vacuum and at elevated temperatures.

2. Description of the Prior Art Many chemical-metallurgical processes have been adapted to be carried out under conditions of reduced pressure or vacuum as batch processes. In batch processes a certain quantity, or batch, of material to be treated is subjected to the desired'treatmennand is then removed from the treatment apparatus to bereplaced by another batch. The same treatment isrepeated individually upon successive batches.

Such batch processes necessitate the restoration of vacuum by pumping out the entire apparatus each time another batch is treated, and have the further drawback that if treatment is carried out at high temperatures, considerable heat losses occur by the cooling of the apparatus between batches. Also, if it is necessary to a conditioning process that an inert gas be used to accelerate cooling as is often the case, gas must be introduced anew for cooling each batch. I

Thus, such batch processes are slow and uneconomical compared with continuous processes. Examples of treatment processes requiring a vacuum are various reactions between solid phases, many metallurgical melting processes, and processes for removinggasfrom metals.

U.S. Pat. No. 2,473,02l discloses a method for the preparation of low-carbonferrochromium by the removal of carbon from high-carbon ferrochromium in a vacuum as a batch process, where both ferrochromium and an oxygen-donating oxide are in a solid state. This operation is carried out at a temperature at which'melting does not occur, for melting would prevent the removal of the reaction gases from the batch, but the temperature must be as high as possible in order to accelerate the process without melting. According 'to the disclosure of this patent the temperature is controlled according to the degree of decarburization, and high-carbon ferrochromium containing from 65 to 75 percent chromium is suitable for this treatment.

According to the method of U.S. Pat. No. 2,473,021, the temperature of the material is kept at a higher level until, with decreasing carbon content, the eutectic temperature is reached on the liquid surface, at which temperature the product melts. The temperature must then be decreased until the carbon content of the batch has passed this region, after which the temperature can again be increased. Therefore decarburization according to this process must be done batchwise, to giveexactly controlled treatment to each batch at dif ferent temperatures for different time periods. If this process were to beattempted in a continuous operation, three separate, individually controllable heating units would be necessary, each to retain the material for a different length of time, which would be highly impractical.

SUMMARY-OF THE INVENTION This invention provides an apparatus and process for continuous heat'treatmentof materials under low pressures, and is particularly advantageous for the decarburization of ferrous alloys as a continuous vacuum process.

In accordance witha preferred embodiment of the invention, decarburization is carried out continuously in two stages, so that a major portion of the carbon in treated material is removed by decarburization in the solid state by heating in a LII permanent ignition furnace. After passingthrou'gh-thepermanent ignition furnace, the product istransferred to a stage where it is melted and spray decarburized, 'whereby the. remaining small carbon content is removed much more.

quickly than it could have been by solid-'state decarbu'rization.

By virtue of themelting the 'product is homogenized, and the remaining oxygen is brought into intimate contact with carbon during the melting stage, permitting simultaneous removal of gas. Melting increases the productdensitwwhich is particularly advantageous if the product-isto. be usedas alloying material in the production of steel.

The apparatus of the invention basically comprises at least two or more vacuum chambers communicating with each other through vacuum-tight doors; The chamber system has. pressure-equalizing chambers communicating with the atmosphere for the introduction anddis'charge of material. pressure-equalizingchambers may also serve as preheating and cooling chambers for the-material, or separate preheating and cooling chambers may be provided.

The vacuum chambers for'the several stages are internally heat insulated, and the outer shell of the apparatus may have a cooling tube arrangement if heat is to be. removed or recovered.

Each individual chamber may be maintainedattemperature and pressure conditions independent of those existing in the other chambers, each'chamb'er being adapted to be pumped materials under controlled conditions of low pressure and elevated temperatures.

A more particular object of the invention is to provide a method and apparatus for continuous decarburization of ferrous alloys by treatment of material in a vacuum.

Other objects and advantages of the invention will become apparent from the following detailed description, taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat schematic overall view, in section, of apparatus according to a preferred form of the invention.

FIG. 2 is a detail view of part of the apparatus of FIG. 1 taken along line 2-2 of FIG. 1 and looking in the direction of the arrows.

FIG. 3 is an expanded sectional view showing a movable vacuum door according to the invention in detail.

FIG. 4 is a view of the double vacuum doors-of the invention taken along line 4-4 of FIG. 3 and looking'in the direction of the arrows.

FIG. 5 is a somewhat schematic sectional view of a ch'arging chamber according to amodified'form of the invention.

FIG. 6 is a view in section of a process chamber according to a modified form of the invention;

FIG. 7 isa transverse sectional ,view of the process chamber of FIG. 6 taken along'line. 7-7and looking inthe direction of thearrows.

FIG. 8 is a sectional view of a discharging and cooling chamber according to the invention.

FIG. 9 is a transverse sectional view of the discharging and cooling chamber of FIG. 8 takenalongline 9-9 andlooking in the direction of the arrows.

DESCRIPTION OF PREFERRED EMBODIMENTS A preferred embodiment of apparatus according to the invention, designated generally by the reference character is shown in FIG. 1. This installation is generally vertically arranged, so that material to be treated is introduced at the upper left, and the product is removed at the bottom. The material to be treated, preferably in the form of a shaped charge as shown at 11, is introduced into a generally cylindrical, pressure-erjualizing, charging chamber 12 through an opening 13 which is fitted with a vacuum-tight lid or cover 14 for tightly sealing the chamber 12 after the charge 1 1 has been introduced. Conventional pressure-sealing gaskets (not shown) may be mounted around the opening to provide an airtight seal.

After a charge 11 has been placed in the charging chamber 12 the air in chamber 12 is pumped out through a vacuum line 15 until the desired degree of vacuum has been reached in the chamber. Within the chamber 12 the charge 11 is seated upon a carriage 16 mounted to roll along a series of rollers 17, some of which are shown in FlG. 1. A pushing mechanism 20, which may be actuated by hydraulic or other suitable means, is mounted to extend into the chamber and has a piston 21 for advancing the charge 11 by pushing the carriage 16, with the charge 11 thereon.

At one end the charging chamber 12 communicates with a generally vertically disposed cylindrical treatment chamber 22 housing a furnace system 23 in the form of a cylindrical tower. Between the charging chamber 12 and the treatment chamber 22 there are a pair of vacuum doors or locks 24 slidably mounted on tracks 25 within a housing 26 for sliding movement to open or closed positions. The doors 24 in their closed position, as shown in FIG. 1, tightly seal the treatment chamber 22 against leakage from the charging chamber 12. When in their open position the vacuum doors 24 are disposed to one side of the path a charge 11 travels when passing from charging chamber 12 to the treatment chamber 22, in an extension of the housing 26 (not shown).

The rollers 17, upon which the carriage 16 bearing a charge 11 travels, continue into the treatment chamber 22, so that the carriage 16 may be pushed by the piston 21 into the treatment chamber 22 when the double vacuum doors 24 are open.

When a charge 11 has been pushed into a position in the upper part of the treatment chamber 22 above the furnace system 23, it is transferred by a charge transfer manipulator 30 from the carriage 16 to the top of a pile 31 of solid charges 11 previously introduced into an open central region 32 of the furnace system 23. The charge transfer manipulator 30 which moves the charges 11 has a movable arm 33 extending into the treatment chamber 22 for engaging and moving the charge, preferably by lifting the charge from the carriage 16, after which the carriage is returned to the charging chamber 11 by the retraction of piston 21. An actuating mechanism driven by hydraulic or other suitable means for moving the arm 33 is mounted outside the chamber 22 as shown at 34.

The furnace system 23 has a generally cylindrical wall 35 of refractory material, which surrounds the open central region 32. Within the furnace wall 35 are an array of heating elements 36. In the embodiment of FIG. 1 the heating elements 36 are shown in the preferred form of a helically disposed radiant heating coil, but some other suitable heating arrangement could be used.

A charge support device 37 serves to support the pile 31 of charges 11 within the furnace system 23 while the charges are exposed to heating by the heating elements 36 therein. The charge support device 37 can be seen to be mounted upon a sturdy bracket 38 capable of holding up a pile 31 of charges through an arm 40 which is extensible to underlie a charge 11 at the bottom of the pile 31. The arm 40 is shown in retracted position in FIG. 1.

When the charge support arm 40 is retracted as shown, a pile 31 of charges can be lowered by a cooperating charge transfer mechanism 41 for removing the lowest charge 11 of the pile 31 to the next treatment stage. The charge transfer mechanism 41 is vertically oriented and has a vertically movable piston member 42 bearing a flat support platform 43 at its upper end for engaging the bottom of the lowermost of the charges 11. A hydraulic cylinder 44 as shown, or some other suitable actuating means, operates the piston 42 to remove the lowermost of the charges 11 in a pile 31 when the charge support arm 40 has been returned to its extended, charge-supporting position beneath the charge 11 just above the lowermost charge 11 while the lowermost charge is removed.

Below the vertical treatment chamber 22 and communicating therewith through an opening 45 is a generally horizontally arranged transmit chamber 46 through which charges 11 travel in a generally horizontal direction during treatment. The transmit chamber 46, like the charging chamber 12 and the vertical heat chamber 22 has a shell 47 of steel or other suitable metal. The upper portion of the transmit chamber 46 has its curved wall lined with an inner layer of refractory brickwork or other suitable heat-shielding material as shown at 48 in FIGS. 1 and 2.

No vacuum-sealing door is shown at the opening 45 between the heat treatment chamber 22 and the transmit chamber 22 and the transmit chamber 46, these two chambers being normally kept at the same low pressure. A vacuum line 50 is shown opening into the chamber 46 for maintaining the desired low pressure.

A carriage 51 riding on tracks 52 provided with roller bearing wheels 53 serves to support and carry the charge 11 thereon through the transmit chamber to a further treatment stage to be described hereafter. The carriage 51 may be generally similar to the carriage 16 of the charging chamber 12, but preferably has a cut out rear portion as shown at 54 in FIG. 2 for slidably surrounding the piston 42 of the charge transfer mechanism 41 so that a charge 11 may be readily lowered on to the carriage at the left-hand end of the chamber. Then the carriage is moved by a drive device 55 to the right in the illustrative embodiment of FIG. 1 to deliver the charge 11 to a position shown in shadow lines at the righthand end of the chamber 46, where another charge transfer manipulator 56 which is similar to the charge transfer manipulator 30, is provided.

An arm 57 of the manipulator 56 lifts the charge 11 from the carriage 51 and lowers the charge through a passage 60 opening from the transmit chamber 46 into a liquid stage heat treatment chamber 61, shown in FIGS. 1 and 2 as a liquid decarburizing chamber. Mounted in the passage 60 for opening and closing the passage are a pair of vacuum-sealing doors 62, which will be discussed in detail later in connection with FIG. 4. A transversely extending generally cylindrical housing 63 is mounted at the passage 60 for receiving the doors 62 when they are in open position. The doors 62 slide sideways on tracks into a portion of the housing when in open position to clear the passage 60 for transferral of the charge 11.

The liquid state heat treatment chamber 61 has a shell of steel or other suitable metal and is generally cylindrical in form, having its axis of rotation in a horizontal direction. Vacuum lines 64, two of which are shown, open at one end of the chamber 61 for sucking out air and gases therein to maintain the desired low pressure in the chamber. Mounted within the chamber 61 is a spray-decarburizing furnace 65. The furnace 65 lies directly below the passage 60 so that a charge 11 transferred by the manipulator 56 can be lowered directly into the furnace 65. The furnace 65 is generally cup-shaped, having an open mouth 67 for feeding in a solid charge 11, insulating sidewalls 68, and a flat bottom 69.

A heating element 72 of generally tubular configuration surrounds the lower portions of the furnace sidewalls 68 as shown in FIG. 1. The heating element 72 is preferably of the radiant heating type, with a coiled resistance element (not shown).

A cover or lid 73 having a small ventilating opening 74 therethrough is mounted for movement to cover or uncover the mouth 67 of the spray decarburization furnace 65. An actuating mechanism for moving the cover 73 is shown at 75 to comprise a piston or arm 76 movable in an horizontal direction by a hydraulic cylinder 77. Of course any suitable closure operator mechanism could be used to actuate the cover 73. The cover 73 is moved aside to the position shown in FIG. 1 when a solid charge 11 is deposited in the furnace 65 and is then returned to its closed position, covering the mouth 67 of the furnace, as the charge 11 is melted.

A spray valve 80 having a spray nozzle 81 opens downwardly through the bottom 69 of the furnace 65 for spraying the melted material of the charge fed into the furnace downwardly into a spray chamber 82 below the liquid stage heat treatment chamber 61. A heating element 83, shown as a radiant heating coil, surrounds the spray. valve 80 for opening the nozzle 81 for passage of the melt and for preventing clogging of the valve 80 and nozzle 81 through solidification of the melted charge material.

The spray chamber 82, a generally cylindrical chamber, has a truncated conical upper portion'84 which extends upwardly into the liquid stageheat treatment chamber 61 to, provide a support for a generally dish-shaped base 85 upon which rest thebase .69 of the spray decarburizing furnace 65 and the heatingelement thereof.

A spray of molten material from the nozzle 8i when the spray valve 80 is open travels down into the spray chamber 82 to be received by a casting mold 86. The casting mold 86 of refractory material as'shown in the illustrative embodiment of FIG. 1 is of the usual cup-shaped form, with an outwardly bent lip 87 around its mouth'88 for catching all of the sprayed material.

Also shown inFlG. l is a secondary furnace 91 which may be provided in cases where there isa danger of premature cooling of the melt. The secondary furnace 91 shown is of the radiant heating type, having a heating element 93, and is surrounded by baffles94. Vacuum lines 97 and 98 open on to the spray chamber 82.

A pressuretight door 95 in the wall of spray chamber 82 per mits the removal of the casting mold 86 when the mold has been filled. As will be discussed, a discharge chamber for pressure equalization could be provided at the outlet or discharge end of the apparatus 10 instead of the door 95.

The several chambers 22,46, 61 and 82 are shown to be I provided with a system of cooling tubes 99, which encircle the outer walls of the chambers. By circulation of a coolant fluid through the tubes 99 the shells or walls of the several chambers may be maintained at arelatively cool temperature, and

heat can be recovered from the treatment process by way of the coolantfluid in a known manner.

The process of decarburization of high-carbon ferrochromium in accordance with theinvention, utilizing the apparatus 1 shown in FIG. 1 will be more readily understood by reference to the following example.

EXAMPLE The material treated was a quantity of carbon containing ferrochromium .having the following analysis by weight: 65.00% Cr; 26.50% Fe; 0.50% Si and 8.00% C.

a. The ferrochromium was ground and oxidized, resulting in a starting mixture analyzed as follows: 61.61% Cr; 24.71% Fe; 0.47% Si; 5.87% C and 8.34% 0. It is noted that the oxygen present in this run was slightly above the theoretical value of 7.95% O. The powdered mixture was moistened with water to I which "a binding agent (C10 had been added and was cast into an annular perforated plate vessel having an inner diameter of cm., an outer diameter of 80 cm. and a height of 40 cm. and was dried, producing a briquette charge ready for carbon removal.

b. The charge was then introduced through the vacuum lid 14 on to the .carriage 16 in the charging chamber 12, whereafter a vacuum was created by pumping out the chamber 12 through the vacuum line 15.

c". The carriage 16-transferred the charge in thevacuum through the double vacuum doors 24 into the vertical-heat treatment chamber 22. Thenthecharge transfer manipulator 30 lifted the charge from-the carriage l6 and transferred it to the top of the pile 31 in the fumace23.

d. In the furnace 23 the charge was heated progressively as it travelled downward. At the permanent ignition zone of; the. furnace, near the heating element 36, the charge wasignit ed so as not to exceed the melting point of its-phases. The charge reached a maximum surface temperature of about l,300. l ,500 C. at the lower portion of the zone of thefurnace. .At that point, the carbon content had been reduced to a low value.

e. The composition of the charge when it reached the transmit chamber 46 after passing through the chamber22 was'as follows: 70.07% Cr; 28.56% Fe; 0.54% Si; 0.10% C and 0.73% O. The weight of the charge had been reduced to 86.5 I% of its original value, indicating that gases (mainly carbon monoxide) had been removed through the vacuum line 50 from the transmit chamber 46. The amount of carbon monoxide removed was [34.9 kg. or 107.9 normal cubic meters ofcarbon monoxide per ton of charge. 0

f. The charge was transferred by means of the mechanisms 51 and 56 through the double vacuum doors 62 to the spray decarburization furnace 65 of the liquid stage heat treatment chamber 61.

g. In the spray decarburization chamber.65,.the charge was quickly melted. At this point the carbon content had alreadyv been significantly reduced. A carbon content of 0.02% by weight was reached, the analysis of the mixture being as follows: 70.20% Cr; 28.62% Fe; 0.54% Si; 0.02% C and 0.62% 0. h. After melting, the heating element 83 of-the spray valve opened the spray nozzle 81 and the melt was disintegrated, a product CXO corresponding to the CO pressure of the environment being reached inthe melt. The temperature of the melt at the start of the spray was about l,650 C. The spraytreated melt was cooled in the casting mold. 86. The analysis of the resulting product was 70.21% Cr; 28.63% Fe; 0.54% Si; 0.61% 0 and 0.009% C. In the melting and spray processes L83 kg. or 1.46 normal cubic meters of carbon monoxide per ton of charge was removed.

Despite the elevated temperature of the .melt,; chrornium losses through the vapor phase were very small. The secondary furnace 91 was not utilized because the .hightemperature of the melt made its use unnecessary.

FIGS. 3-8 show a modified form of apparatus according to the invention, in which the several process chambers are generally horizontally arranged. Several important features of the invention appear in both the horizontal form of FIGS. 3-6 and in the form shown in FIGS. 1. and 2.. -Such a feature is the double vacuum-sealing door arrangement, such doors being generally designated 24 and 62 and in the embodiment of FIGS. 1 and 2 and which in FIGS.3.-5 are designated l03.

Referring now to FIGS. 3 and 4 showing the double vacuum doors 103 in greater detail, it can be seenthat the doors:103 are generally circular in plan and are somewhat convex to resist pressure pushing inward toward the evacuated chambers. The doors 103 are enclosed within a housing 104 which is elongated to provide an enclosedspace in which the doors 103 may be moved sideways when in. open position to clear a path for transferral of treated material betweenchambers which the doors 103 serve to isolate when in closed, sealing position. The doors M separating the charging chamber 12 fromthe vertical treatment chamber 22 and the doors 62 ofiFIG. l are generally similar in structure and operation to. the doors 103, and also have elongated housings to permit similarsideways movement, the doors 62 having a housing 63 as, shown in FIG. 2.

The operating mechanism of the double vacuum doors103 comprises a generally boxlike central body 110, mounted for sliding movement upon pairs of upper and lower rails 11] and 112 respectively. The central body 110 supports both doors 103 on opposite sides thereof. Each door 103 comprises a convex, generally circular plate 105 having a returned peripheral edge 106 for tightly engaging a sealing groove;l07

extending around a door frame r reveal 108. An aperture 113 centrally disposed in the door plate 105 receives an rearwardlyopen cuplike fitting 114 having a flattened base 115. Received within the fittings 114 are tubular studs 116, 116 which are slidably movable into and out of a hollow tube 117 extending through the boxlike support body 110 for movement of the doors 103 toward and away from the body 110 in opening and closing.

As shown in FIG. 4, the stud 116 is smaller in diameter than the stud 116 so that the smaller stud may be telescopically received within the larger stud. Within the cuplike fittings 114 the ends of the 116, 116' are engaged by bearing elements (not shown) which allow some leeway for final tightening of the doors 103. Conventional ball bearings and cone ball bearings are suitable for this purpose. Suitable bracing elements 118 surround the aperture 113 to reinforce the door panel 105 at the central portion thereof around the fitting 114.

The doors 103 are operated by hydraulic cylinder devices 120, mounted in the boxlike support body 110, for example, as shown in FIG. 3 where three such cylinders 120 are shown disposed at 120 angles to each other. Only one cylinder for each door 103 is illustrated in FIG. 4 for the sake of clarity. A piston 121 of each cylinder 120 is connected to a shaft 122 to which a transversely extending arm 123 is secured. The arms 123 are, in turn, secured to the studs 116, 116' to push and pull the doors 103, through the studs 116, 116 in and out upon movement of the pistons 121 in their cylinders 120.

Thus in closing the doors 103 the pistons 121 move outwardly under hydraulic pressure, pushing the doors 103 away from the body 110, until the returned door edges 106 are tightly pressed into the respective sealing grooves 107 of the door frame or reveal 108. Suitable gaskets in the grooves 107 seal the closures. Pumping out of the chambers closed by the doors 103 further tightens the closure, the bearings in the fittings 114 allowing the doors 103 to be pulled into place by the vacuum. In all respects thus far discussed, the doors 62 resemble the doors 103.

When the doors 103 are in open position near the body 110 the entire assembly is moved sideways along the rails 111, 112. As shown in FIGS. 3 and 4, the body 110 is secured at its lower portion to an elongated channel member 126 which is provided with wheels 127 rotatably mounted on axles 128 secured to the legs of the channel for rolling along the lower rails 112, which are preferably in the form of I-beams. Downwardly extending shafts 130 having bearings 131 engaging the inner sides of the tracks 112 to prevent displacement of the wheels 127 from the tracks 112. An arrangement of shafts and bearings 130', 131 at the upper part of the body 110 serves to guide the body between upper tracks 111, which are preferably formed as angles. As shown in FIG. 3, a locking pin 132 may be provided to extend through the housing 103 to lock the body 110 in place against sliding motion when the doors 103 are aligned with the frame 108. The double vacuum doors 62 have a similar sliding movement, though of course, there are modifications in the mounting structure suited to the horizontal position of the doors 62. The necessary modifications of the sliding arrangement of doors 62 of FIGS. 1 and 2 will be obvious to those skilled in the art in view of the detailed description of the arrangement of FIG. 4.

The several portions of the horizontally arranged metallurgical treatment apparatus are shown in FIGS. 3-8, with FIGS. 3 and 4 showing the double vacuum doors which have been described. FIG. 5 shows the input end of the apparatus, FIGS. 6 and 7 show a horizontally arranged process chamber, and FIGS. 8 and 9 show the discharge end of the apparatus.

Referring to FIG. 5, the horizontal form of the apparatus is seen to have a charging chamber 134 of generally cylindrical form, into which a charge 135, resting on a pallet or base 136, can be'introduced through a vacuum lid 137. A charge-advancir ig arrangement (not shown) which may be similar to that provided in the charging chamber 12 of FIG. 1, serves to advance the charge 135 resting on its base 136 through the double vacuum doors 103 into a heat treatment chamber 138 after the pressure in the chambers 134 and 138 has been equalized and the double vacuum doors have been opened. Atter the charge 135 has been advanced into the heat treatment chamber 138, the double vacuum doors 103 are closed, and another charge 135 may be introduced into the charging chamber 134 so that material may be processed in a continuous operation.

The heat treatment chamber 138 is generally in the form of a horizontally oriented cylinder in which there is a processing furnace 139, as best seen in FIGS. 6 and 7. The furnace 139 has walls 140 and a roof 141 of refractory brickwork or other suitable heat-resistant material. The furnace structure is reinforced by means of a rigid frame structure generally indicated by the reference character 143. As shown in FIGS. 6 and 7, the frame structure 143 of the furnace is mounted on a series of wheels to roll along a sturdy bed 146 within the chamber 138, so that the entire furnace 139 with its frame structure 143 may be rolled out of the chamber 138 for inspection and repair when required by simply disconnecting the charging chamber 134 from the heat treatment chamber 138 and pulling out the furnace frame structure 143.

A vacuum line 147 opens onto the heat treatment chapter 138 for evacuating the chamber so that the desired low pressure can be provided for treatment of the charge 135 in,the furnace 139. The furnace 139 is preferably heated by radiant means through heating coils (not shown) similar to those used in the embodiment of FIG. 1.

A series of charges 135 on their bases 136 is shown in shadow lines in FIG. 6, with an arrow indicating their direction of travel through the furnace 139. Each charge base 136 has two longitudinally extending runners, shown formed as I- beams in FIG. 7, which contact a series of transversely arranged rotating shafts 151 to drive the bases 136 with the charges 135 thereon through the furnace. A conventional motor (not shown) is positioned outside the chamber 138 to protect the motor from heat and is coupled to the shafts 15 1 to rotate the shafts 151.

The housing 104 of a second pair of double vacuum doors 103 is indicated at the right-hand, or output end of the chamber 138 in FIG. 6. A second heat treatment chamber similar to that of FIG. 6 could be positioned after the heat treatment chamber 138 and isolated therefrom by the second pair of double vacuum doors 103 for the performance of a successive heat treatment stage at different temperature and/or pressure. It is contemplated that for certain metallurgical treatment processes a plurality of heat treatment chambers like the chamber 138 would be provided for individually and separately treating a series of charges through several process steps.

An important feature of the invention is that continuous treatment of a series of successive charges 135, fed into the apparatus individually through the charging chamber 135, is readily effected without undesirable losses of heat or vacuum.

FIGS. 8 and 9 show a combined cooling and discharge chamber, generally indicated by the reference numeral 152.

- After passing through the heat treatment chamber 138, or

through the last of a series of such chambers, as discussed above, it may be desirable to cool the treated material of the charges before removing the charges from the apparatus. The chamber 152 is thus provided for cooling the charges and equalizing pressure for discharge. At the left-hand end of chamber 152 the housing 104 of a final pair of double vacuum doors 103 is shown, through which the charges 135.0n their bases 136 are advanced into the chamber 152. The chamber 152 is basically cylindrical in form, and has a continuation of the series of rotating shafts 151 for advancing the charges 135 through contact with the runners 150. A motor 153 for rotating the shafts 151 is shown in FIG. 9. Unlike the motor for driving the shafts 151 in the heat treatment chamber, the motor 153 may be positioned within the chamber itself since there is no danger of heat damage.

An array of cooling tubes or pipes 154 surrounds the path of the charges 135 through the cooling chamber 152. In FIG. 8

only a section of the array 154 of cooling tubes is shown for the sake of clarity, with arrows indicating the direction of travel of a cooling fluid through the tubes. As shown in FIG. 9, the array of cooling tubes 154 is generally in the fonn of an inverted U, so that the charges 135 can be advanced with their bases 136 passing between the arms of the U. The array of cooling tubes 154 preferably comprises relatively large longitudinally extending coolant feed pipes 155 and a series of smaller tubes 156.

At its right-hand, or output end, the discharge and cooling chamber 152 has a vacuum-sealing lid 157 for allowing removal of a treated charge from the apparatus. The discharge lid 157 is generally similar to the vacuum lid 137 of the charging chamber and to the lid 14 of the embodiment of FIG. 1. The cooling chamber, as well as the charging chamber and intermediate heat treatment chambers, are all provided with suitable vacuum pipes or mains for providing the desired low pressure. In the case of the charging chamber 134 and the discharge chamber 152, relief valves (not illustrated) are also provided for equalizing pressures. Such a cooling and discharge chamber could be provided at the discharge end of the apparatus of FIG. 1.

The housings 104 of the double vacuum doors 103 may also be provided with vacuum pipes or conventional pressure relief valves for pressure equalization between chambers. At appropriate places, gaskets or other suitable sealing members are provided to prevent leakage.

The mode of operation of the modified form of the apparatus as shown in FIGS. 3-9 is basically similar to that of the form shown in FIGS. 1 and 2 and described above. The form of FIGS. 1 and 2 is especially suited for decarburization of ferrous alloys, and is therefore provided with the advantageous spray decarburization chamber and furnace. The form shown in FIGS. 3-9 is ,contemplated to be more effective for heat treatment of materials in the solid state, of proper bases 136 in the form of vessels for the charges, charge material could be reduced to the molten state by means of treatment in the modified form of the apparatus.

Also contemplated is the heat treatment of various materials in which an atmosphere containing a special composition of gases, such as inert gases, is required at some process stage or stages. It will be clear that any desired atmosphere can be provided at any treatment stage through the use of the apalthough by provision paratus of the invention by the use of suitable conduits for introducing gases if desired. The advantageous arrangement of double vacuum-sealing doors between successive chambers pennits isolation of the treatment steps from each other and thereby makes possible the precise control of process parameters at each stage of treatment.

Because of the self-contained nature of the system according to the invention, automatic remote control of the several advancing and transferral mechanisms, as well as the opening and closing of the vacuum doors may readily be provided. Suitable conventional remote control arrangements and circuits will suggest themselves to those skilled in the art, so no particular cybernetic control system has been set forth as part of this invention.

It will be clear to those skilled in this art that the practice of the invention lends itself readily to various modifications. The specific practice described is only set forth by way of illustration. What is disclosed is a highly effective method and apparatus for continuous treatment of various materials at conditions of low pressure and elevated temperature.

What is claimed is:

1. A continuous process of decarburization of ferrous material comprising separately introducing individual charges of ferrous material to be treated into a heat treatment chamber through a pressure-equalization chamber, heat treating the material at low pressure and at a temperature below the melting point of said material in the heat treatment chamber for reducing the carbon content of the material, transferring the heat treated material into a spray decarburizatio n furnace isolated from said heat treatment chamber and quickly reducing the material to a molten state under conditions of low pressure for further reduction of the carbon content of the material, disintegrating the molten material by spraying the material through a nozzle for still further reducing the carbon content of the material, and collecting the treated material in a casting mold.

2. The method of claim 1 wherein the maximum temperature in said heat treatment chamber is in the range of from about l,300 to 1,500 C. and the temperature of the molten material in the spray decarburization furnace reaches a maximum of about 1,650 C.

3. The method of claim 2 wherein the treated material is ferrochrome. 

2. The method of claim 1 wherein the maximum temperature in said heat treatment chamber is in the range of from about 1,300* to 1, 500* C. and the temperature of the molten material in the spray decarburization furnace reaches a maximum of about 1,650* C.
 3. The method of claim 2 wherein the treated material is ferrochrome. 